A control valve is a fundamental component in fluid conduction systems, whose applications vary from pressure reduction, cooling, phase separating, emergency relief and double block and bleed, to regulation and control of the fluid conduction. Typically, the valve is required to be capable of sealing a fluid flow line across a pressure drop and permitting fluid flow therethrough as required. The differential pressure between upstream and downstream could be enormous, up to as much as 200 bar. On the other hand, the very same valve might be required to operate at a much lower differential pressure when the same system is operating in another mode. Similarly, the temperatures of the fluid in such a system could range from below 0.degree. C. to 580.degree. C.
Control valves for use at high differential pressure are known in the art. These include butterfly valves, V-ball valves and globe valves. These valves suffer from a number of disadvantages. Many are unable to function at high pressure differentials. Others are sensitive to high temperatures. Generally, these valves start to leak after several months.
One suggested solution is the "Camflex" valve, manufactured by Masoneilan of Dresser Industries, Inc., U.S.A., which comprises an eccentric rotating plug for sealing the inlet into the valve. The plug is actuated by a spring-opposed rolling diaphragm actuator coupled to the plug by a rotatable cam, thus providing a multiplication of forces for sealing the plug.
The Camflex suffers from the disadvantage that, due to the actuation of the cam, a relatively massive actuator is required to overcome the opposed torque resulting from the differential pressure of the flow. As a consequence, the Camflex is limited as to the differential pressure under which it is operative.